Finding the previous value of a field in Dataset

hi, How can I find that the value in the drop down is changed ? The requirement is: There is a Drop down list and a button on the page. On click of button store the value present in the drop – down in the typed Datset. Now this Dataset is passed to a function. Functionality of these function : I need to find out that these data that I have stored in the Typed dataset is Changed or not. For these I need to know the original values the Dataset was holding , so that I can do comparison. Issue: Is there any mechanism to find the previous data that these dataset was holding ? Thanks - techiDam